So-called "autodepositing coating" compositions, which first appeared in the patent literature in the early 1970's, are compositions that are effective in forming on a metallic surface immersed therein an organic coating which increases in thickness as a function of the length of time the surface ("substrate") is immersed in the composition ("bath") in the absence of an externally-applied electrical potential. By way of illustration, autodepositing coating compositions and methods of autodeposition are disclosed in U.S. Pat. Nos. 3,585,084; 3,592,699; 3,776,848; 3,791,431; 3,795,546; 3,829,371; 3,839,097; 3,914,519; 3,936,546; 3,955,532; 3,960,610; 4,012,351; 4,030,945; 4,103,049; 4,104,424; and 4,103,817. The prior art autodepositing compositions are generally employed at a pH of between about 1.6 and about 3.8.
The present autodepositing coating composition differ from the above-mentioned prior art compositions inasmuch as the present compositions contain persulfate and are capable of autodepositing coating in a pH range of from about 4 to about 8.5, thereby making autodeposition possible at neutral or near-neutral pH's.